From a7b692e8edf4b855d2096c9abd24179866bfb279 Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Wed, 14 Sep 2016 19:05:40 +0300
Subject: [PATCH] PR #1954 improvements.

Inverted the direction of move-by-wheel, so that scrolling down will
move you forward through the photos or documents overview.

Added an accumulation of the scroll amount so that you don't zoom or
skip photos each time a (possibly very frequent) wheel event fires.
---
 Telegram/SourceFiles/mediaview.cpp | 31 ++++++++++++++++++------------
 Telegram/SourceFiles/mediaview.h   |  2 ++
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/Telegram/SourceFiles/mediaview.cpp b/Telegram/SourceFiles/mediaview.cpp
index bf2b6a1f7..635c9166c 100644
--- a/Telegram/SourceFiles/mediaview.cpp
+++ b/Telegram/SourceFiles/mediaview.cpp
@@ -1890,20 +1890,27 @@ void MediaView::keyPressEvent(QKeyEvent *e) {
 }
 
 void MediaView::wheelEvent(QWheelEvent *e) {
-	if (e->delta() < 0) {
-		if (e->modifiers().testFlag(Qt::ControlModifier)) {
-			zoomOut();
-		} else {
-			if (e->source() == Qt::MouseEventNotSynthesized) {
-				moveToNext(-1);
+	constexpr auto step = static_cast<int>(QWheelEvent::DefaultDeltasPerStep);
+
+	_verticalWheelDelta += e->angleDelta().y();
+	while (qAbs(_verticalWheelDelta) >= step) {
+		if (_verticalWheelDelta < 0) {
+			_verticalWheelDelta += step;
+			if (e->modifiers().testFlag(Qt::ControlModifier)) {
+				zoomOut();
+			} else {
+				if (e->source() == Qt::MouseEventNotSynthesized) {
+					moveToNext(1);
+				}
 			}
-		}
-	} else {
-		if (e->modifiers().testFlag(Qt::ControlModifier)) {
-			zoomIn();
 		} else {
-			if (e->source() == Qt::MouseEventNotSynthesized) {
-				moveToNext(1);
+			_verticalWheelDelta -= step;
+			if (e->modifiers().testFlag(Qt::ControlModifier)) {
+				zoomIn();
+			} else {
+				if (e->source() == Qt::MouseEventNotSynthesized) {
+					moveToNext(-1);
+				}
 			}
 		}
 	}
diff --git a/Telegram/SourceFiles/mediaview.h b/Telegram/SourceFiles/mediaview.h
index 3f8756b39..ff1e85b6a 100644
--- a/Telegram/SourceFiles/mediaview.h
+++ b/Telegram/SourceFiles/mediaview.h
@@ -322,6 +322,8 @@ private:
 	typedef QMap<OverState, anim::fvalue> ShowingOpacities;
 	ShowingOpacities _animOpacities;
 
+	int _verticalWheelDelta = 0;
+
 	void updateOverRect(OverState state);
 	bool updateOverState(OverState newState);
 	float64 overLevel(OverState control) const;